Let’s face it: when it comes to social networking, Facebook is the only game in town. MySpace and other early networks are a speck in its rear view mirror. Everyone is on Facebook: your friends, your ex-girlfriend, your mom and dad, the people you went to high school with and never want to see again, and just about everybody else in the world. Official membership is somewhere over the 300 million mark, roughly the population of the United States.

Facebook wants to be more than just one of the top destinations of the web–sometimes even beating out Google. It wants to be the web, with everything coming into and out of your Facebook account. This includes using Word, for instance, and I’ll bet that Facebook will put out a sophisticated search tool sometime soon.

The problem is, interest in Facebook is waning. Not plummeting (like, say, the interest in Second Life), but slowly eroding. One sure indication of this gradual erosion: teen users are getting fed up. The recent Teens and Social Network Study by roiworld shows that teenagers are getting sick of Facebook. Money quote:

Online teens in the US report they typically spend 2 hrs on the internet a day. On average, 80% of that time is spent on a social network. Is Facebook the new MySpace? Most online teens belong to a social net, and Facebook is still by far their #1 social network. But, a significant amount of teens report “Facebook Fatigue.” Among those teens who have created a profile, roughly one-in-five (19%) claim “they no longer visit Facebook” or “are using it less than they did a year ago.”

Teens who quit Facebook or lessen their use do so because too many adults have joined (like parents and teachers) and because of fears of privacy violation. Here is one provocative chart from the report: